1. Field of the Invention
This invention relates to photoresist compositions that can exhibit enhanced properties, including optimized iso-dense bias of imaged lines. In particular, preferred resists of the invention contain an added acid reaction component which has been found can modulate desired iso-dense bias of imaged lines. Preferred resists of the invention contain an ester-based solvent such as ethyl lactate or propylene glycol methyl ether acetate in addition to the acid reaction component.
2. Background
Photoresists are photosensitive films for transfer of images to a substrate. They form negative or positive images. After coating a photoresist on a substrate, the coating is exposed through a patterned photomask to a source of activating energy such as ultraviolet light to form a latent image in the photoresist coating. The photomask has areas opaque and transparent to activating radiation that define an image desired to be transferred to the underlying substrate. “Chemically amplified” photoresist compositions have been employed for higher performance applications. Such photoresists may be negative-acting or positive-acting and rely on multiple crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In other words, the photogenerated acid acts catalytically. See, for example, U.S. Pat. Nos. 6,680,159; 6,042,997; 5,075,199; 4,968,851; 4,883,740; 4,810,613; and 4,491,628.
Certain additives have been included in photoresist compositions to improve lithographic performance. See, for instance, U.S. Pat. Nos. 6,743,563; 6,727,049; 6,607,870; and 6,300,035.
For lithographic imaging of features having submicron dimensions, the iso-dense effects can become more prominent. The iso-dense effects result in a difference in transfer dimension for dense features as compared to features that are more spaced apart. A developed resist line or other feature is generally considered “isolated” herein if it is spaced from the closest adjacent resist feature a distance equal to three or more times the line width. Thus, e.g., if a line is printed at a 0.25 μm width, that line would be considered isolated (rather than dense) if the next adjacent resist feature was spaced at least about 0.75 microns from the line. Common resolution problems with isolated lines include rounded tops and undercutting.
Thus, it can be problematic to achieve desired transfer of images of both dense and isolated lines in the same imaged field. See, for instance, U.S. Pat. No. 6,667,136, which discusses that it can be difficult to make isolated and nested structures print as identically as desired resulting in an undesirable condition known as across chip line width variation.
It thus would be desirable to have new photoresist compositions. It would be particularly desirable to have new photoresist compositions that can enable control of iso-dense bias of imaged features.